#include <iostream>
using namespace std;

class A
{
public:
    explicit A(int i = 5):m_a(i)
    {

    }
    void show_number();
private:
    int m_a;
};

void A::show_number()
{
    cout << "m_a is :" << m_a << endl;
}

int main()
{
    A s;
    // s = 10;
    // explicit可以抑制内置类型隐式转换,不能直接赋值
    s = A(20);
    s.show_number();
}